Power transmission system of hydraulically driven working vehicle

ABSTRACT

A power transmission system of a hydraulically driven working vehicle comprises: a prime mover supported by a vehicle frame, the prime mover including a prime mover output shaft projecting in the fore-and-aft direction of the vehicle; a pump housing; a hydraulic pump disposed in the pump housing, the hydraulic pump including a pump shaft projecting from the pump housing in the fore-and-aft direction of the vehicle so as to be drivingly connected to the prime mover output shaft; a first hydraulic motor disposed outside the pump housing so as to be fluidly connected to the hydraulic pump; a transaxle supported by one of front and rear portions of the vehicle frame, the transaxle including a transaxle housing, a pair of axles disposed in the transaxle housing so as to be driven by the hydraulic motor, and a differential gear unit disposed in the transaxle housing so as to be drivingly interposed between the hydraulic motor and the pair of axles; a PTO shaft; and a working power train extracting a part of power transmitted from the prime mover output shaft to the pump shaft and transmitting the extracted power to the PTO shaft.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/433,551 filed May 15, 2006, which is hereby incorporated in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a power transmission system for a hydraulicallydriven working vehicle, especially, for a large-size vehicle.

2. Related Art

Conventionally, there is a well-known hydraulically driven workingvehicle, equipped with a hydraulic pump disposed in a housing anddrivingly connected to a prime mover (engine), and with a hydraulicmotor disposed outside the housing and fluidly connected to thehydraulic pump so as to drive an axle. U.S. Pat. No. 6,732,828 disclosesan example of this type of vehicle, wherein a hydraulic pump is disposedin a pump housing, a hydraulic motor for driving an axle is disposed ina transaxle housing separated from the pump housing, and a belttransmission system is interposed between a vertical output shaft of anupright engine and a working device.

The upright arrangement of the prime mover (engine) with the verticaloutput shaft is available because the vehicle is small-sized,particularly, in the fore-and-aft direction. If a working vehicle havingsuch an arrangement of hydraulic pump and motor is large-sized,horizontal arrangement of a prime mover (engine) with a horizontal shaftis advantageous for ensuring a large space for other equipment includinga working device (such as a midship mower) in the vertical direction.However, the thing to be considered is layout of a power transmissionsystem for drivingly connecting the prime mover to the hydraulic pumpand the working device without hindering arrangement, attachment anddetachment of the working device.

SUMMARY OF THE INVENTION

An object of the invention is to provide an advantageous powertransmission system for a working vehicle, among a prime mover, ahydraulic pump, a hydraulic motor for driving an axle and a workingdevice, wherein the hydraulic pump is disposed in a housing and thehydraulic motor is disposed outside the housing so as to be fluidlyconnected to the hydraulic pump.

To achieve the object, a power transmission system of a hydraulicallydriven working vehicle according to the present invention comprises: aprime mover supported by a vehicle frame, the prime mover including aprime mover output shaft projecting in the fore-and-aft direction of thevehicle; a pump housing; a hydraulic pump disposed in the pump housing;a first hydraulic motor disposed outside the pump housing so as to befluidly connected to the hydraulic pump; a first transaxle supported byone of front and rear portions of the vehicle frame; a first power takeoff shaft (a first PTO shaft); and a working power train. The hydraulicpump includes a pump shaft projecting from the pump housing in thefore-and-aft direction of the vehicle so as to be drivingly connected tothe prime mover output shaft. The first transaxle includes a firsttransaxle housing, a pair of first axles disposed in the first transaxlehousing so as to be driven by the first hydraulic motor, and a firstdifferential gear unit disposed in the first transaxle housing so as tobe drivingly interposed between the first hydraulic motor and the pairof first axles. The working power train extracts a part of powertransmitted from the prime mover output shaft to the pump shaft andtransmits the extracted power to the first PTO shaft.

The power transmission system is available for various arrangementsabout the driving connection between the prime mover and the hydraulicpump, the working power train, the first transaxle, etc., withouthindering arrangement, attachment and detachment of a working devicedriven by the first PTO shaft.

With respect to arrangement about the driving connection between theprime mover and the hydraulic pump, preferably, a propeller shaft isdrivingly interposed between the prime mover output shaft and the pumpshaft, thereby ensuring a flexible driving connection between the primemover and the hydraulic pump with little power loss.

Alternatively, a belt transmission is drivingly interposed between theprime mover output shaft and the pump shaft, thereby ensuring a simpleand flexible driving connection between the prime mover and thehydraulic pump.

Alternatively, the pump shaft is directly connected to the prime moveroutput shaft, thereby ensuring a minimized driving connection betweenthe prime mover and the hydraulic pump with little power loss.

With respect to arrangement of the working power train, preferably, theworking power train includes a gear train, thereby reducing power loss.

Alternatively, the working power train includes a belt transmission,thereby being simple and flexible.

Preferably, the power transmission system further comprises a secondpower take off shaft (a second PTO shaft) to which the working powertrain also transmits the extracted power, thereby being available fordriving a device in addition to a working device drivingly connected tothe first PTO shaft.

Preferably, the power transmission system further comprises a coolingfan disposed on the pump shaft or on a shaft directly connected to thepump shaft, thereby efficiently cooling the pump housing incorporatingthe hydraulic pump in a small space and with components saved in number.

Preferably, the first hydraulic motor is disposed in the first transaxlehousing, thereby minimizing the power transmission system.

Preferably, the first differential gear unit is a bi-directive clutchtype differential gear unit. Therefore, differential drive of the firstaxles is automatically canceled when either of the drive wheels providedon the respective first axles slips, thereby ensuring traction abilityand safety of the vehicle in a bad ground condition.

Alternatively, the first differential gear unit includes at least one ofa limited slip differential element and a differential lock element.Therefore, differential drive of the first axles is automatically ormanually canceled when either of the drive wheels provided on therespective first axles slips, thereby ensuring traction ability andsafety of the vehicle in a bad ground condition.

Preferably, the power transmission system further comprises: a secondtransaxle supported by the other rear or front portion of the vehicleframe. The second transaxle includes a second transaxle housing, a pairof second axles disposed in the second transaxle housing, and a pair ofsecond hydraulic motors disposed in the second transaxle housing so asto be fluidly connected to the hydraulic pump and to drive therespective second axles. Therefore, the vehicle can travel by four-wheeldrive so as to increase traction ability.

Alternatively, the power transmission system further comprises: a secondtransaxle supported by the other rear or front portion of the vehicleframe. The second transaxle includes a second transaxle housing, a pairof second axles disposed in the second transaxle housing, a secondhydraulic motor disposed in the second transaxle housing so as to befluidly connected to the hydraulic pump, and a second differential gearunit disposed in the second transaxle housing so as to be drivinglyinterposed between the second hydraulic motor and the pair of secondaxles. Therefore, the vehicle can travel by four-wheel drive so as toincrease traction ability.

Preferably, the second differential gear unit is a bi-directive clutchtype differential gear unit. Therefore, differential drive of the secondaxles is automatically canceled when either of the drive wheels providedon the respective second axles slips, thereby ensuring traction abilityand safety of the vehicle in a bad ground condition.

Alternatively, the second differential gear unit includes at least oneof a limited slip differential element and a differential lock element.Therefore, differential drive of the second axles is automatically ormanually canceled when either of drive wheels provided on the respectivesecond axles slips, thereby ensuring traction ability and safety of thevehicle in a bad ground condition.

These, further and other objects, features and advantages will appearmore fully from the following description with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view of an entire hydraulic four-wheel driveworking vehicle equipped with a power transmission system according to afirst embodiment of the present invention.

FIG. 2 is a sectional plan view of the entire hydraulic four-wheel driveworking vehicle according to the first embodiment.

FIG. 3 is a hydraulic circuit diagram of the hydraulic four-wheel driveworking vehicle.

FIG. 4 is a hydraulic circuit diagram of an alternative rear transaxleto be adapted to the hydraulic circuit of FIG. 3.

FIG. 5 is a hydraulic circuit diagram of an alternative front transaxleto be adapted to the hydraulic circuit of FIG. 3.

FIG. 6 is a hydraulic circuit diagram of another alternative fronttransaxle to be adapted to the hydraulic circuit of FIG. 3.

FIG. 7 is a sectional side view of an entire hydraulic four-wheel driveworking vehicle equipped with a power transmission system according to asecond embodiment of the present invention.

FIG. 8 is a sectional plan view of the entire hydraulic four-wheel driveworking vehicle according to the second embodiment.

FIG. 9 is a sectional side view of a working power train of the vehicleaccording to the second embodiment.

FIG. 10 is a schematic front view of the working power train of thevehicle according to the second embodiment.

FIG. 11 is a sectional side view of an entire hydraulic four-wheel driveworking vehicle equipped with a power transmission system according to athird embodiment of the present invention.

FIG. 12 is a sectional plan view of the entire hydraulic four-wheeldrive working vehicle according to the third embodiment.

FIG. 13 is a sectional side view of an entire hydraulic four-wheel driveworking vehicle equipped with a power transmission system according to afourth embodiment of the present invention.

FIG. 14 is a sectional plan view of the entire hydraulic four-wheeldrive working vehicle according to the fourth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, a hydraulic four-wheel drive working vehicle100 according to a first embodiment of the invention will be described.Vehicle 100 is an Ackerman type steered lawn tractor, comprising: aframe 3; a rear transaxle 1 supported by a rear portion of frame 3; afront transaxle 2 supported by a front portion of frame 3; an engine 10supported by frame 3 between front and rear transaxles 1 and 2; a pumphousing 60 supported by frame 3; and a mower 20 (an example of a workingdevice driven by engine 10) vertically movably suspended below frame 3.Frame 3 includes a pair of left and right vertical side plate portions3L and 3R (as shown in FIG. 2) extended substantially in thefore-and-aft direction. Rear transaxle 1 and pump housing 60 aredisposed in the inside space of frame 3 between the left and right sideplate portions 3L and 3R.

In vehicle 100, pump housing 60 incorporating a variable displacementhydraulic pump P (see FIG. 3) is supported by the rear portion of frame3 just above rear transaxle 1. In each of later-discussed vehicles 200,300 and 400, pump housing 60 is disposed at a position different fromthat of vehicle 100.

Rear transaxle 1 includes a rear transaxle housing 1H incorporating a(fixed displacement) hydraulic motor M1 driven by hydraulic pump P, leftand right rear axles 6, a differential gear unit 38 (see FIG. 3)differentially connecting axles 6 to each other, and a deceleration geartrain 37 (see FIG. 3) drivingly interposed between hydraulic motor M1and differential gear unit 38. Alternatively, hydraulic motor M1 may bedisposed outside rear transaxle housing 1H and pump housing 60, ifhydraulic motor M1 can be fluidly connected to hydraulic pump P. Leftand right rear axles 6 project laterally outward from rear transaxlehousing 1H so as to be fixedly provided on tips thereof with respectiverear wheels 7 serving as unsteerable drive wheels.

Front transaxle 2 includes a front transaxle housing 2H pivoted at alateral middle top portion thereof onto frame 3 through a center pivot 5so as to be vertically movable at left and right ends thereof. Fronttransaxle housing 2H incorporates a pair of left and right hydraulicmotors M2 and M3. Left and right front wheel support units 48L and 48Rare steerably provided on left and right ends of front transaxle housing2H, respectively. Axles 8 are supported by respective front wheelsupport units 48L and 48R, and left and right front wheels 9 are fixedon respective axles 8 so as to serve as steerable drive wheels.

Engine 10 is supported by frame 3 through vibro-isolating rubbers 43 anddisposed in a bonnet 11. A radiator fan 44 and a radiator 42 are mountedon frame 3 just in front of engine 10 in bonnet 11.

A dashboard is formed just behind bonnet 11. A steering wheel 12 isextended upwardly rearward from the dashboard, and operatively connectedto a steering control valve disposed in a valve casing 12 a (see FIG.3). The steering control valve is fluidly connected to a power steeringcylinder 79 operatively connected to front wheel support units 48L and48R, so that front wheel support units 48L and 48R, i.e., front wheels 9are steered by rotating steering wheel 12.

A speed control pedal 13 and a brake pedal (not shown) are disposed at afoot portion of the dashboard. Speed control pedal 13 is a seesaw pedalhaving oppositely movable front and rear portions with a pivottherebetween. The front portion of pedal 13 is to be depressed forsetting forward traveling speed, and the rear portion of pedal 13 is tobe depressed for setting backward traveling speed. A speed control lever14 is pivoted on pump housing 60 so as to interlock with a movable swashplate Pa of hydraulic pump P in pump housing 60, and is operativelyconnected to speed control pedal 13, so that the rotational directionand speed of rear wheels 7 (and front wheels 9) is controlled by thedepression direction and degree of speed control pedal 13.

A rear cover 15 is mounted on a rear portion of frame 3, and a driver'sseat 16 is mounted on the top of rear cover 15. A reservoir tank 28 isdisposed in rear cover 15 just below seat 16. Reservoir tank 28 isprovided at the top thereof with an oiling port which also serves as abreather.

Mower 20 is disposed under frame 3 between rear wheels 7 and frontwheels 9. Left and right mower hungers 91 are extended from front endportions of the left and right side plate portions 3L and 3R of frame 3,respectively, and connected to the front end of mower 20 throughrespective link rods 91 a, thereby vertically movably suspending mower20.

Mower 20 incorporates rotary blades 20 a, and is provided at the topthereof with a gearbox 20 d for driving rotary blades 20 a. A mowerinput shaft projects rearward from gearbox 20 d so as to be drivinglyconnected to a later-discussed mid PTO shaft 54.

A grass collection device (not shown) can be optionally connected to arear end portion of vehicle 100 and a duct D can be optionallyinterposed between mower 20 and the grass collection device, so as tocollect grass mowed by rotary blades 20 a in mower 20. Duct D isextended upwardly rearward from a right portion of mower 20 andconnected at the rear end thereof to the grass collection device. A ductfan (not shown) is disposed in duct D so as to absorb the grass mowed byrotary blades 20 a and to blow the grass to the grass collection devicethrough duct D. The duct fan is drivingly connected to a later-discussedrear PTO shaft 55.

When duct D is attached to vehicle 100, duct D is disposed in the insideof frame 3 along the right side plate portion 3R of frame 3. To ensurethis rightward eccentric arrangement of duct D, as shown in FIG. 2, reartransaxle 1, pump housing 60, reservoir tank 28, a power transmissionsystem for transmitting power from engine 10 to hydraulic pump P andmower 20, hydraulic pressure fluid pipes extended from pump housing 60and rear transaxle 1, and top gearbox 20 d of mower 20 are disposed inthe inside of frame 3 leftward from (laterally opposite to) duct D.

The power transmission arrangement between engine 10 and hydraulic pumpP and mower 20 will be described with reference to FIGS. 1 to 3. Asshown in FIGS. 1 and 2, engine 10 includes a horizontal output shaft 53projecting rearward from a flex coupling damper 47 at the rear end ofengine 10. Output shaft 53 is disposed at the lateral center of frame 3between the left and right side plate portions 3L and 3R of frame 3.

As shown in FIGS. 1 and 2, vertical and lateral plate-shaped crossmember 3 a is spanned between the left and right side plate portions 3Land 3R of frame 3. Pump housing 60 is fixed onto a rear surface of crossmember 3 a so as to be cantilevered rearward from cross member 3 a.Hydraulic pump P includes a horizontal pump shaft 17 projecting forwardfrom pump housing 60 through cross member 3 a. A pair of fluidsuction-and-delivery ports 61 and 62 are disposed on a top surface ofpump housing 60.

A propeller shaft 56 is interposed between output shaft 53 of engine 10and pump shaft 17. Propeller shaft 56 is connected at a front endthereof to the rear end of output shaft 53 through a universal joint 58,and at a rear end thereof to the front end of pump shat 17 throughanother universal joint 58. Referring to FIG. 2, when viewed in plan,pump shaft 17 is slightly offset leftward from output shaft 53 so as tobe prevented from interfering with duct D, so that propeller shaft 56 isslightly inclined rearwardly leftward. Further, referring to FIG. 1,when viewed in side, pump shaft 17 is disposed slightly lower thanoutput shaft 53, so that propeller shaft 56 is slightly inclinedrearwardly downward.

As shown in FIGS. 1 and 2, rear transaxle housing 1H is disposedleftwardly downward from pump housing 60 and fixed to the left sideplate portion 3L of frame 3. A pair of fluid suction-and-delivery ports1 a and 1 b are disposed on a right side surface of rear transaxlehousing 1. A pipe 81 is interposed between port 61 on pump housing 60and port 1 b on rear transaxle housing 1H.

Differential gear unit 38 is provided with a limited slip differential(LSD) element 38 a and a differential lock element 38 b. Differentiallock element 38 b is manually operated so as to lock axles 6 to eachother, i.e., cancel the differential rotation of axles 6, therebytransmitting torque to rear wheel 7 slipping in mud or a ditch. However,even when differential lock element 38 b is not operated fordifferential lock, LSD element 38 a transmits a considerable amount ofpower to the slipping wheel 7. LSD element 38 a can be any type element,such as an element including a pair of helical planetary gears, or aviscous coupling type element. Differential gear unit 38 may be providedwith either LSD element 38 a or differential lock element 38 b.Alternatively, differential gear unit 38 may be a normal differentialgear unit with neither LSD element 38 a nor differential lock element 38b.

Alternatively, the differential gear unit disposed in rear transaxlehousing 1H may be a bi-directive clutch type differential gear unit 138,as shown in FIG. 4, which can automatically transmit power to rear wheel7 slipping in mud or a ditch.

Referring to front transaxle 2, hydraulic motor M2 is fixed indisplacement, and hydraulic motor M3 is variable in displacement.Alternatively, both the hydraulic motors for driving respective axles 8may be variable in displacement.

Variable displacement hydraulic motor M3 is provided with a movableswash plate M3 a (see FIG. 3). A cam mechanism CM interlocking withswash plate M3 a is disposed along the rear surface of front transaxlehousing 2H. In this embodiment, the right hydraulic motor for right axle8 is variable displacement hydraulic motor M3. Therefore, cam mechanismCM is disposed rearwardly leftward of front transaxle housing 2Havailably for connection to swash plate M3 a.

Referring to FIG. 2, left and right front wheel support units 48L and48R are connected to each other through a tie rod 89. Cam mechanism CMis connected to one of front wheel support units 48L and 48R (in thisembodiment, right front wheel support unit 48R) through a link 46, so asto transmit left or right turning of front wheel support units 48L and48R to movable swash plate M3 a. Therefore, when steerable front wheels9 are steered by rotating steering wheel 12, the tilt angle of movableswash plate M3 a is reduced so as to accelerate axles 8 (front wheels9), thereby ensuring smooth turning of vehicle 100 without dragging ofwheels 9.

Referring to FIG. 2, power steering cylinder 79 is disposed along theoutside surface of a front portion of the left side plate portion 3L offrame 3. A bracket 48 a is fixed on left front wheel support unit 48L(opposite to right front wheel support unit 48R connected to cammechanism CM), and a piston rod 90 of power steering cylinder 79 ispivoted at the front tip thereof onto bracket 48 a. The telescopicmovement of piston rod 90 of power steering cylinder 79 is controlled bythe steering control valve in valve casing 12 a based on the rotationdirection and angle of steering wheel 12 so as to turn left front wheelsupport unit 48L, thereby also turning right front wheel support unit48R through tie rod 89.

A pair of fluid suction-and-delivery ports 2 a and 2 b are disposed onthe rear left surface of front transaxle housing 2H laterally oppositeto cam mechanism CM. A pipe 23 is interposed between port 2 a and port 1a on rear transaxle housing 1H, and a pipe 26 is interposed between port2 b and port 62 on pump housing 60. Pipes 23 and 26 are extended alongthe left side plate portion 3L of frame 3. In this way, pump housing 60,rear transaxle housing 1H and front transaxle housing 2H are mutuallyfluidly connected through pipes 81, 23 and 26.

A working power train for driving an attached working device such asmower 20 will be described. As shown in FIGS. 1 and 2, a pulley 49 isfixed on a portion of pump shaft 17 projecting forward from cross member3 a. A pulley 50 is supported onto the front surface of cross member 3 adownwardly leftward from pulley 49. A belt 51 is interposed betweenpulleys 49 and 50. A tension clutch (not shown) is interposed betweenpulleys 49 and 50, so as to selectively tighten belt 51 to transmittorque of pulley 49 to pulley 50 or loosen belt 51 to isolate pulley 50from torque of pulley 49. Pulley 50 has a forwardly projectinghorizontal pulley shaft serving as mid PTO shaft 54. Gearbox 20 d onmower 20 is disposed in front of mid PTO shaft 54, and a propeller shaft57 is interposed between mid PTO shaft 54 and the input shaft projectingrearward from gearbox 20 d through respective universal joints 59.

Pump shaft 17 is extended rearward so as to have a portion projectingrearward from pump housing 60, serving as a rear PTO shaft 55. A clutchbox can be connected to rear PTO shaft 55, and the above-mentioned ductfan in duct D can be drivingly connected to rear PTO shaft 55.

In this way, a part of power transmitted from engine 10 to pump shaft 17for driving hydraulic pump P is extracted to transmitted to mid PTOshaft 54 and rear PTO shaft 55, so as to drive working devices drivinglyconnected to respective PTO shafts 54 and 55.

In the embodiment shown in FIGS. 1 and 2, a cooling fan 52 is fixed onrear PTO shaft 55 (the rearwardly extended portion of pump shaft 17) soas to blow air forward onto pump housing 60. The cooling air fromcooling fan 52 is reflected by cross member 3 a so as to also cool reartransaxle housing 1H. In this way, the number of components for coolingpump housing 60 and rear transaxle housing 1H is saved by providingcooling fan 52 on the extended portion of pump shaft 17 serving as rearPTO shaft 55.

Referring to FIG. 3, an HST circuit HC1 of vehicle 100 will bedescribed. As mentioned above, pipe 81 is interposed between port 61 ofpump housing 60 and port 1 b of rear transaxle housing 1H, pipe 23 isinterposed between port 1 a of rear transaxle housing 1H and port 2 a offront transaxle housing 2H, and pipe 26 is interposed between port 2 bof front transaxle housing 2H and port 62 of pump housing 60.

In pump housing 60, a passage 65 is interposed between hydraulic pump Pand port 61, and a passage 66 is interposed between hydraulic pump P andport 62. It is defined that, during forward travel of vehicle 100, thedelivery port of hydraulic pump P is connected to passage 65 and port61, and the suction port of hydraulic pump P to passage 66 and port 62.

In rear transaxle housing 1H, a passage 22 is interposed betweenhydraulic motor M1 and port 1 a, and a passage 21 is interposed betweenhydraulic motor M1 and port 1 b.

In front transaxle housing 2H, a passage 24 is extended from port 2 aand bifurcated into passages 24 a and 24 b connected to respectivehydraulic motors M2 and M3, and a passage 25 is extended from port 2 band bifurcated into passages 25 a and 25 b connected to respectivehydraulic motors M2 and M3.

In this way, HST circuit HC1 is configured so that hydraulic motor M1for driving rear axles 6 and the pair of hydraulic motors M2 and M3 fordriving front axles 8 are fluidly connected in series to hydraulic pumpP, and hydraulic motors M2 and M3 are fluidly connected in parallel tohydraulic pump P so as to differentially drive front axles 8.

When vehicle 100 travels forward (speed control pedal 13 is depressedfor forward traveling), fluid delivered from hydraulic pump P issupplied to hydraulic motor M1 through passage 65, port 61, pipe 81,port 1 b and passage 21, subsequently supplied to hydraulic motors M2and M3 through passage 22, port 1 a, pipe 23, port 2 a and passage 24(passages 24 a and 24 b), and returned to hydraulic pump P throughpassage 25 (passages 25 a and 25 b), port 2 b, pipe 26, port 62 andpassage 66. In other words, during forward travel of vehicle 100, ports61, 1 a and 2 b serve as delivery ports, and ports 62, 1 b and 2 a serveas suction ports. When vehicle 100 travels backward, the fluid supplyroute is reversed, so that ports 61, 1 a and 2 b serve as suction ports,and ports 62, 1 b and 2 a serve as delivery ports.

An unshown drive mode switching valve may be disposed across pipes 23and 26. The valve is shiftable between a two-wheel drive position and afour-wheel drive position. When the valve is disposed at the four-wheeldrive position, the valve thoroughly opens pipe 23 between ports 1 a and2 a, and pipe 26 between ports 2 b and 62, thereby supplying hydraulicmotors M2 and M3 with fluid delivered from hydraulic pump P. When thevalve is disposed at the two-wheel drive position, the valve bypassesbetween ports 1 a and 62 so as to circulate fluid between hydraulic pumpP and hydraulic motor M1 without supplying hydraulic motors M2 and M3with fluid from hydraulic pump P. Simultaneously, the valve disposed atthe two-wheel drive position bypasses between ports 2 a and 2 b so as toallow the free rotation of hydraulic motors M2 and M3 isolated fromhydraulic pressure supplied by hydraulic pump P.

Pump housing 60, rear transaxle housing 1H and front transaxle housing2H are filled therein with fluid so as to serve as respective fluidsumps. Pump housing 60 is provided with a drain port 63, rear transaxlehousing 1H is provided with a drain port 1 c, and front transaxlehousing 2H is provided with a drain port 2 c. Reservoir tank 28 isconnected to drain port 63 through a pipe 70, to drain port 1 c througha pipe 29, and to drain port 2 c through a pipe 30, so as to absorbexcessive fluid from any of pump housing 60, rear transaxle housing 1Hand front transaxle housing 2H, when the corresponding fluid sump isexcessively expanded.

Pump housing 60 incorporates a charge pump 69, which is driven togetherwith hydraulic pump P by pump shaft 17. In this regard, pump shaft 17penetrates hydraulic pump P and charge pump 69 so as to project forwardto serve as the input shaft drivingly connected to engine 10, and toproject rearward to serve as rear PTO shaft 55. A suction port 64 isopened on pump housing 60, and connected to reservoir tank 28 through apipe 72 outside pump housing 60, and to charge pump 69 through a passage71 in pump housing 60. A filter 73 is provided on an intermediateportion of pipe 72.

In pump housing 60, a charge fluid passage 67 is extended from chargepump 69 and connected to passages 65 and 66 through respective checkvalves 68, so as to supply fluid delivered from charge pump 69 tolower-pressurized one of passages 65 and 66. A pressure-regulating valve74 is connected to passage 67 at the upstream side of check valves 68 soas to drain excessive fluid to the fluid sump in pump housing 60.

Incidentally, a hydraulic fluid source of the steering control valve invalve casing 12 a is omitted in FIG. 3. Preferably, instead of chargefluid passage 67 connected to passages 65 and 66, the fluid deliveredfrom charge pump 69 may be extracted from pump housing 60 to be suppliedto the steering control valve, and subsequently, the fluid may beintroduced into pump housing 60 so as to be supplied to either ofpassages 65 and 66.

In front transaxle housing 2H, a check valve 40 is connected to passage24 a so as to supply fluid from the fluid sump in front transaxlehousing 2H to passage 24 a at the upstream side of hydraulic motor M2during forward travel of vehicle 100, thereby preventing cavitationcaused by dragging of front wheels 9 by rear wheels 7.

The parallel connected hydraulic motors M2 and M3 may be replaced with acombination of variable displacement hydraulic motor M2 and adifferential gear unit 82, as shown in FIG. 5. Differential gear unit 82is driven by hydraulic motor M2 and differentially connects axles 8 toeach other. In front transaxle housing 2H shown in FIG. 5, differentialgear unit 82 is provided with a limited slip differential (LSD) element82 a and a differential lock element 82 b. Differential lock element 82b is manually operated so as to lock axles 8 to each other, i.e., cancelthe differential rotation of axles 8, thereby transmitting torque tofront wheel 9 slipping in mud or a ditch. However, even whendifferential lock element 82 b is not operated for differential lock,LSD element 82 a transmits a considerable amount of power to theslipping wheel 9. LSD element 82 a can be any type element, such as anelement including a pair of helical planetary gears, or a viscouscoupling type element. Differential gear unit 82 may be provided witheither LSD element 82 a or differential lock element 82 b.Alternatively, differential gear unit 82 may be a normal differentialgear unit with neither LSD element 82 a nor differential lock element 82b.

Differential gear unit 82 shown in FIG. 5 may be replaced with abi-directive clutch type differential gear unit 83 as shown in FIG. 6,which is clutched off for establishing the two-wheel drive mode duringnormal travel of vehicle 100, and is automatically clutched on forestablishing the four-wheel drive mode when the travel condition ofvehicle 100 becomes abnormal.

Alternatively, in vehicle 100, transaxle 2 supporting steerable wheels 9may serve as a rear transaxle supporting steerable rear wheels,transaxle 1 supporting unsteerable wheels 7 may serve as a fronttransaxle supporting unsteerable front wheels, and engine 10 may bedisposed between transaxles 1 and 2 so as to have output shaft 53projecting forward to be drivingly connected to hydraulic pump P in pumphousing 60 disposed in front of engine 10.

Alternative vehicle 200 will be described with reference to FIGS. 7 to10. Parts and components having the same function as those of vehicle100 are designated by the same reference numerals. A PTO gearbox 201 isfixed onto the left side plate portion 3L of frame 3. Pump housing 60 isfixed onto a front surface of PTO gearbox 201 so as to transmit power tothe gear train in PTO gearbox 201. Pump shaft 17 projects forward frompump housing 60. A propeller shaft 256 is interposed between outputshaft 53 of engine 10 and pump shaft 17 through respective universaljoints 58. Pump shaft 17 projects rearward from pump housing 60 into PTOgearbox 201 so as to serve as an input shaft 202 of the gear train inPTO gearbox 201.

A counter shaft 211, a mid PTO shaft 254 and a rear PTO shaft 255 arerotatably disposed in PTO gearbox 201 in the fore-and-aft direction (inparallel to input shaft 202). Mid PTO shaft 254 is disposed downwardlyleftward (in FIG. 10, downwardly rightward) from input shaft 202 andprojects forward from PTO gearbox 201. Rear PTO shaft 255 is disposedleftward (in FIG. 10, rightward) from input shaft 202 and projectsrearward from PTO gearbox 201.

In PTO gearbox 201, clutches 209 and 210 are drivingly interposed inseries between input shaft 202 and PTO shafts 254 and 255. Clutch 209 isselectively clutched on for transmitting power from input shaft 202 toclutch 210, or clutched off for isolating power of input shaft 202 fromclutch 210. Clutch 210 is selectively clutched on for transmitting powerof counter shaft 110 to rear PTO shaft 255, or clutched off forisolating power of counter shaft 110 from rear PTO shaft 255.

More specifically, in PTO gearbox 201, a gear 211 a is fixed on countershaft 211, and gears 254 a and 255 a are fixed on respective PTO shafts254 and 255. A gear 209 a is relatively rotatably provided on inputshaft 202 and constantly meshes with gear 211 a. Clutch 209 isinterposed between gear 209 a and input shaft 202. Clutch 209 isselectively clutched on for not-relatively rotatably engaging gear 209 ato input shaft 202 to thereby drive counter shaft 211, or clutched offfor disengage gear 209 a from input shaft 202 to thereby shut offrotation of input shaft 202 from counter shaft 211.

A gear 210 a is not relatively rotatably provided on counter shaft 211and constantly meshes with gear 254 a. That is, mid PTO shaft 254 isdriven by input shaft 202 unless clutch 209 is clutched off andregardless of whether clutch 210 is clutched on or off. A gear 210 b isrelatively rotatably provided on a boss portion of gear 210 a andconstantly meshes with gear 255 a. Clutch 210 is interposed betweencounter shaft 211 and gear 210 b. Clutch 210 is selectively clutched onfor not relatively rotatably engaging gear 210 b to counter shaft 211 tothereby drive rear PTO shaft 255, or clutched off for disengaging gear210 b from counter shaft 211 to thereby shut off rotation of countershaft 211 from rear PTO shaft 255.

A propeller shaft 257 is interposed between mid PTO shaft 254 and theinput shaft projecting rearward from gearbox 20 d on mower 20 throughrespective universal joints 59 so as to transmit power of mid PTO shaft254 to rotary blades 20 a.

When duct D with the duct fan is attached onto vehicle 200, the duct fanis drivingly connected to rear PTO shaft 255. Due to clutch 210 in PTOgearbox 201, another clutch does not have to be interposed between rearPTO shaft 255 and a device for driving the duct fan.

A cooling fan 203 is fixed on the forward projecting portion of pumpshaft 17 in front of pump housing 60. Cooling fan 203 blows air rearwardto pump housing 60 and the front surface of PTO gearbox 201, so as tocool hydraulic pump P in pump housing 60 and the gears and clutches inPTO gearbox 201. Cooling fan 203 also blows air to pipes 26 and 81disposed adjacent to cooling fan 203, thereby efficiently cooling fluidcirculating in HST circuit HC1.

Further, input shaft 202 (the rearward extended portion of pump shaft17) projects rearward from PTO gearbox 201 so as to be fixedly providedthereon with a cooling fan 204. Cooling fan 204 blows air forward to therear surface of PTO gearbox 201, so as to effect cooling of PTO gearbox201 with the assistance of cooling fan 203. The rear surface of PTOgearbox 201 reflects the air blown from cooling fan 204 rearward towardrear transaxle housing 1H, thereby cooling components in rear transaxlehousing 1H. Alternatively, cooling fan 204 may blow air rearward towardrear transaxle housing 1H.

Pump housing 60, PTO gearbox 201, rear transaxle housing 1H, mowergearbox 20 d, reservoir tank 28 and pipes 23, 26 and 81 are laterallyeccentrically collected (leftward) so as to ensure optional arrangementof duct D in a (rightward) space laterally opposite to these powertransmission components.

The above-mentioned alternative arrangements adaptable to vehicle 100,such as bi-directive clutch type differential gear unit 135 in reartransaxle 1 and the combination of hydraulic motor M3 and differentialgear unit 82 or 83 in front transaxle 2, are also adaptable to vehicle200.

Alternative vehicle 300 will be described with reference to FIGS. 11 and12. Parts and components having the same function as those of vehicle100 are designated by the same reference numerals. An engine 310 ismounted on the front portion of frame 3, similar to engine 10 of vehicle100 or 200. Engine 310 includes a horizontal rear output shaft 353projecting rearward from the rear end surface of engine 310 at a lateralmiddle portion between the left and right side plate portions 3L and 3Rof frame 3. Engine 310 also includes a horizontal front output shaft 382projecting forward from the front end surface of engine 310. Therotation direction of output shafts 353 and 382 is the same as that ofoutput shaft 53 of engine 10.

A vertical support plate 311 is fixed onto the rear end surface ofengine 310 and extended rightward from the portion fixed to engine 310.Pump housing 60 is fixed onto a front surface of the rightward extendedportion of support plate 311 so as to be disposed on the right side ofengine 310 and along the right side plate portion 3R of frame 3.

Pump shaft 17 projects rearward (in the fore-and-aft direction) frompump housing 60 through support plate 311 so as to be laterally alignedwith output shaft 353 of engine 310 in parallel. A pulley 349 is fixedon rear engine output shaft 353, and a pulley 350 is fixed on therearward projecting portion of pump shaft 17. A belt 351 is interposedbetween pulleys 349 and 350, so as to transmit power from engine 310 tohydraulic pump P in pump housing 60. Radiator fan 44 in front of engine310 may be used for cooling pump housing 60.

Rear transaxle 1 and front transaxle 2 in vehicle 300 are configured anddisposed similar to those of vehicle 100 or 200, so that the rotationaldirection of axles 6 relative to the fluid suction and deliverydirection of hydraulic motor M1 and the rotational direction of axles 8relative to the fluid suction and delivery direction of hydraulic motorsM2 and M3 in vehicle 300 are the same as those of vehicle 100 or 200.Namely, during forward travel of vehicle 300, ports 1 a and 2 b serve asdelivery ports, and ports 1 b and 2 a serve as suction ports.

The rotational direction of swash plate Pa and speed control lever 14relative to the depression of speed control pedal 13 in vehicle 300 isreversed so as to be opposite to that of vehicle 100 or 200, inconsideration that the rotation direction of pump shaft 17 in vehicle300 is opposite to that in vehicle 100 or 200 because pump housing 60 isreversed in the fore-and-aft direction. Consequently, during forwardtravel of vehicle 300, port 61 serves as the delivery port, and port 62serves as the suction port, similar to those in vehicle 100 or 200.Thus, vehicle 300 employs HST circuit HC1 with the same fluidcirculation route such that hydraulic pump P supplies fluid to hydraulicmotor M1 in rear transaxle 1 prior to hydraulic motors M2 and M3 infront transaxle 2 during forward travel of vehicle 300.

In this regard, pipe 81 interposed between ports 61 and 1 b is extendedalong the right side plate portion 3R of frame 3 (rightward from ductD), pipe 23 interposed between ports 1 a and 2 a is extended along theleft side plate portion 3L of frame 3 (leftward from duct D), and pipe26 interposed between ports 62 and 2 b is extended substantiallylaterally so as to pass through a space between the bottom end of engine310 and a later-discussed propeller shaft 357 below engine 310, therebyconstituting HST circuit HC1.

A mid PTO shaft 386 projects rearward from pulley 385 through anelectromagnetic clutch 388, and a front PTO shaft 387 projects forwardfrom pulley 385. A mower 320 is suspended and disposed similar to mower20, however, mower 320 is provided on the top thereof with a mowergearbox 320 d from which an input shaft projects forward toward mid PTOshaft 386 in front of gearbox 320 d. Propeller shaft 357 is interposedbetween mid PTO shaft 386 and the forward projecting input shaft ofmower gearbox 320 d through respective universal joints 59.

Electromagnetic clutch 388 may be replaced with a tension clutchinterposed between pulleys 383 and 384. One of PTO shafts 386 and 387may be removed. The belt-and-pulley type working power train may bereplaced with a gear train interposed between output shaft 382 and PTOshafts 386 and 387. Alternatively, a working power train for drivingrotary blades in mower 320 may be configured so as to transmit powerfrom pump shaft 17. In this case, an electromagnetic clutch may beprovided onto pulley 350, or a belt tension clutch may be disposed so asto control the tension of belt 351.

While rear transaxle housing 1H and reservoir tank 28 are disposedlaterally opposite to duct D disposed rightward in the inside of frame3, pump housing 60 and the working power train are disposed forward fromduct D, so as to expand a free space leftward of duct D.

The above-mentioned alternative arrangements adaptable to vehicle 100,such as bi-directive clutch type differential gear unit 135 in reartransaxle 1 and the combination of hydraulic motor M3 and differentialgear unit 82 or 83 in front transaxle 2, are also adaptable to vehicle300.

Alternative vehicle 400 will be described with reference to FIGS. 13 and14. Parts and components having the same function as those of vehicles100 and 300 are designated by the same reference numerals.

Arrangements of engine 310 having opposite output shafts 353 and 382,mid and front PTO shafts 386 and 387, and the working power traininterposed between front engine output shaft 382 and PTO shafts 386 and387 are the same as those of vehicle 300.

In vehicle 400, a support member 411 is attached onto the rear surfaceof engine 310 so as to support pump housing 60. Pump shaft 17 projectsforward from pump housing 60 so as to be directly connected to rearengine output shaft 353. Therefore, the rotational direction of pumpshaft 17, the fluid suction and delivery direction of hydraulic pump Pand the tilt direction of movable swash plate Pa relative to thedepression direction of speed control pedal 13 is the same as that ofvehicle 100 and 200. Thus, vehicle 400 employs HST circuit HC1 and thepiping including pipes 23, 26 and 81, as shown in FIG. 3.

In this regard, on the assumption that the arrangement and configurationof front and rear transaxles 1 and 2 are similar to those in vehicles100, 200 and 300, pipe 26 interposed between ports 61 and 2 b, pipe 81interposed between ports 62 and 1 b, and pipe 23 interposed betweenports 1 a and 2 a are collected leftward from engine 310 and along theleft side plate portion 3L of frame 3 so as to be prevented frominterfering with engine 310 and the working power train for driving therotary blades in mower 320, and ensure a rightward space in the insideof frame 3 for arrangement of duct D.

Pump shaft 17 further projects rearward from pump housing 60 so as to befixedly provided thereon with cooling fan 52 for cooling pump housing60.

The above-mentioned alternative arrangements adaptable to vehicles 100and 300, such as bi-directive clutch type differential gear unit 135 inrear transaxle 1, the combination of hydraulic motor M3 and differentialgear unit 82 or 83 in front transaxle 2, and the gear train betweenengine output shaft 382 and PTO shafts 386 and 387, are also adaptableto vehicle 400.

It is further understood by those skilled in the art that the foregoingdescription is a preferred embodiment of the disclosed apparatus andthat various changes and modifications may be made in the inventionwithout departing from the spirit and scope thereof defined by thefollowing claims.

1. A vehicle power transmission system comprising: a prime moversupported by a vehicle frame, the prime mover including a prime moveroutput shaft projecting in the fore-and-aft horizontal direction of thevehicle; a pump housing; a hydraulic pump disposed in the pump housing,the hydraulic pump including a pump shaft projecting from the pumphousing in the fore-and-aft horizontal direction of the vehicle so as tobe drivingly connected to the prime mover output shaft; a hydraulicmotor disposed outside of the pump housing so as to be fluidly connectedto the hydraulic pump; a transaxle supported by one of front and rearportions of the vehicle frame, the transaxle including a transaxlehousing, a pair of axles disposed in the transaxle housing so as to bedriven by the hydraulic motor, and a differential gear unit disposed inthe transaxle housing so as to be drivingly interposed between thehydraulic motor and the pair of axles; a power take off shaft (a PTOshaft) extended in the fore-and-aft horizontal direction of the vehicle;a working unit having an input shaft extended in the fore-and-afthorizontal direction of the vehicle; a propeller shaft interposedbetween the PTO shaft and the input shaft of the working unit; and adrive train extracting a part of power transmitted from the prime moveroutput shaft to the pump shaft so as to transmit the extracted power tothe PTO shaft.
 2. The vehicle power transmission system according toclaim 1, wherein a gear train serving as the drive train includes adrive shaft, which is extended in the fore-and-aft horizontal directionof the vehicle so as to be driven by the pump shaft, and gears, whichare interposed between the drive shaft and the PTO shaft so as totransmit power from the drive shaft to the PTO shaft.
 3. The vehiclepower transmission system according to claim 2, further comprising: apropeller shaft interposed between the prime mover output shaft and thepump shaft.
 4. The vehicle power transmission system according to claim2, further comprising: a cooling fan provided on the pump shaft.
 5. Thevehicle power transmission system according to claim 2, wherein thedrive shaft is extended coaxially to the pump shaft and is connected tothe pump shaft so as to be rotatably integral with the pump shaft. 6.The vehicle power transmission system according to claim 2, furthercomprising: a gear housing incorporating the gear train and supportingthe PTO shaft, wherein the pump housing is fixed to the gear housing soas to drivingly connect the pump shaft to the drive shaft.
 7. Thevehicle power transmission system according to claim 2, wherein the PTOshaft serves as a first PTO shaft, and wherein the vehicle powertransmission system further comprises: a second power take off shaft (asecond PTO shaft), wherein the gear train further includes a gear fortransmitting power from the drive shaft to the second PTO shaft.
 8. Thevehicle power transmission system according to claim 7, furthercomprising: a cooling fan provided on the second PTO shaft.
 9. Thevehicle power transmission system according to claim 7, furthercomprising: a gear housing incorporating the gear train and supportingthe first and second PTO shafts, wherein the pump housing is fixed tothe gear housing so as to drivingly connect the pump shaft to the driveshaft.
 10. The vehicle power transmission system according to claim 9,wherein the first and second PTO shafts projects outward from the gearhousing opposite to each other.
 11. The vehicle power transmissionsystem according to claim 2, wherein the hydraulic motor serves as afirst hydraulic motor, the transaxle serves as a first transaxle, andthe pair of axles serve as first axles, and wherein the vehicle powertransmission system further comprises: a second transaxle supported bythe other rear or front portion of the vehicle frame, the secondtransaxle including a second transaxle housing, a pair of second axles,which are disposed in the second transaxle housing, and a pair of secondhydraulic motors, which are disposed in the second transaxle housing soas to be fluidly connected to the hydraulic pump and to drive therespective second axles.
 12. The vehicle power transmission systemaccording to claim 2, wherein the hydraulic motor serves as a firsthydraulic motor, the transaxle serves as a first transaxle, the pair ofaxles serve as first axles, and the differential gear unit serves as afirst differential gear unit, and wherein the vehicle power transmissionsystem further comprises: a second transaxle supported by the other rearor front portion of the vehicle frame, the second transaxle including asecond transaxle housing, a pair of second axles, which are disposed inthe second transaxle housing, a second hydraulic motor, which isdisposed in the second transaxle housing so as to be fluidly connectedto the hydraulic pump, and a second differential gear unit, which isdisposed in the second transaxle housing so as to be drivinglyinterposed between the second hydraulic motor and the pair of secondaxles.
 13. The vehicle power transmission system according to claim 1,wherein the prime mover output shaft serves as a first prime moveroutput shaft, wherein the prime mover further includes a second primemover output shaft, which projects opposite to the first prime moveroutput shaft so as to be rotatably integral with the first prime moveroutput shaft, and wherein a belt drive train serving as the drive trainincludes a belt interposed between the second prime mover output shaftand the PTO shaft.
 14. The vehicle power transmission system accordingto claim 13, wherein the pump housing is fixed to the prime mover, andwherein the pump shaft is extended coaxially to the first prime moveroutput shaft and is connected to the first prime mover output shaft soas to be rotatably integral with the first prime mover output shaft. 15.The vehicle power transmission system according to claim 14, furthercomprising: a cooling fan provided on the pump shaft.
 16. The vehiclepower transmission system according to claim 13, wherein the pump shaftis extended parallel to the first prime mover output shaft, and whereinthe vehicle power transmission system further comprises: another drivetrain interposed between the first prime mover output shaft and the pumpshaft.
 17. The vehicle power transmission system according to claim 16,wherein a belt drive train serving as said other drive train includes abelt interposed between the first prime mover output shaft and the pumpshaft.
 18. The vehicle power transmission system according to claim 13,wherein the hydraulic motor serves as a first hydraulic motor, thetransaxle serves as a first transaxle, and the pair of axles serve asfirst axles, and wherein the vehicle power transmission system furthercomprises: a second transaxle supported by the other rear or frontportion of the vehicle frame, the second transaxle including a secondtransaxle housing, a pair of second axles, which are disposed in thesecond transaxle housing, and a pair of second hydraulic motors, whichare disposed in the second transaxle housing so as to be fluidlyconnected to the hydraulic pump and to drive the respective secondaxles.
 19. The vehicle power transmission system according to claim 13,wherein the hydraulic motor serves as a first hydraulic motor, thetransaxle serves as a first transaxle, the pair of axles serve as firstaxles, and the differential gear unit serves as a first differentialgear unit, and wherein the vehicle power transmission system furthercomprises: a second transaxle supported by the other rear or frontportion of the vehicle frame, the second transaxle including a secondtransaxle housing, a pair of second axles, which are disposed in thesecond transaxle housing, a second hydraulic motor, which is disposed inthe second transaxle housing so as to be fluidly connected to thehydraulic pump, and a second differential gear unit, which is disposedin the second transaxle housing so as to be drivingly interposed betweenthe second hydraulic motor and the pair of second axles.